The use of implantable pacing and defibrillation devices to treat or prevent various cardiac problems has become relatively widespread. Several difficulties with such treatments relate to placement and durability of electrodes. Typically, well practiced, careful and gentle maneuvers are required during insertion to avoid breaking the leads and/or electrodes. Once placed, leads may fracture after being subjected to repeated stresses as the heart beats and the patient moves. Leads and electrodes may also migrate from their desired position.
For transvenous implantation, a lead is typically introduced by advancing it through a vein to a location in or near the heart with the aid of fluoroscopy. The lead is then anchored to heart tissue or a passive anchor mechanism, such as a tine, is utilized to prevent the lead from moving. The heart tissue will tend to form around the lead, attenuating sensed signals as well as altering pacing and/or defibrillating thresholds. Because implantation requires traversing the vasculature as well as placement and anchoring within the heart, many problems can arise.
Many lead insertion techniques push a lead into place into tissue or through the vasculature. Pushing the lead stresses the lead and can cause lead failure. With vascular implantations, the pathway is defined but is subject to constrictions and tight turns. Non-vascular implantation calls for tunneling through existing tissue. While extra stiffness may help with lead insertion and aid accurate lead placement, stiffer leads create their own problems with migration, perforation, and fracture. As stiffness increases, the ability of the lead to inadvertently perforate tissue rises. Further, with extra stiffness, the lead does not rest in place during muscle movement, tending to increase the size of any associated fibroid, and potentially leading to migration.